1. Field of the Invention
This invention relates to a material for a molded article and film having liquid or gas barrier property, more particularly to a material for a molded article having a liquid or gas barrier property to be used for fluid treatment such as delivery of fluid, storage or filtration of fluid, etc. such as a tube, tank, strainer, various covers, etc., and a material for a polyamide film having a excellent gas barrier property, transparency, slippage characteristic as well as the rigidity necessary for post-working such as lamination, printing, bag-making, etc., and methods for producing these materials.
2. Background Information
Polyamide resins have been widely utilized as injection and extruding molding materials for parts particularly of automobiles and electrical goods, because their molded articles have excellent mechanical properties.
However, polyamide resins have the property of permitting liquids or gases particularly such as water, alcohols, Freon gases, gasoline, etc. to permeate therethrough, posing various problems due to this property. For example, when a tube made of nylon is used as the Freon tube concerned with a freezing device, Freon is permeated therethrough, whereby there ensues the problem that the Freon within the device will be reduced; when a tank made of nylon is used as the brake tank in the field of automobiles, there is the problem that water will be incorporated into the brake fluid; and when a tank made of nylon is used as the gasoline tank, the problem occurs that water is incorporated into gasoline. Also, even when a gasoline tank consisting of two or more layers of polyethylene and nylon may be used, if the nylon layer is too thin, gasoline still permeates therethrough, whereby a problem may be caused which does not comply with environmental pollution regulations, etc.
For solving such problems, there have been made attempts to satisfy the standards by superposing a plurality of layers of resins with different barrier properties from each other. However, these also involve such a problem that the steps for producing molded articles are complicated, and also that still a fully satisfactory barrier property cannot be obtained.
The molded article of the polyamide resin of the prior art has various problems due to permeation of liquid or gas as described above.
While the molded articles of polyamide resins have been used as described above, polyamide films have been used mainly in the field of food packaging because of various excellent characteristics such as transparency, pinhole resistance, gas barrier property, heat resistance and oil resistance, etc.
Such polyamide films may be classified into unstretched films and stretched films. Polyamide films, which are inferior in water vapor barrier property and heat sealability, are frequently used as the film laminated with polyolefins by such means as co-extrusion or lamination.
In recent years, further improvement of gas barrier property has been demanded in food packaging, and the gas barrier property of polyamide films cannot be said to be sufficient depending on the use. Particularly, under highly humid conditions, the gas barrier property of polyamide films will be noticeably lowered. For this reason, there have been practiced co-extrusion molding of ethylene-vinyl alcohol copolymer (EVOH) excellent in gas barrier property with polyamide, or coating of polyvinylidene chloride (PVDC) with good gas barrier property on the surface of polyamide film. However, not only because such EVOH and PVDC are expensive, but also partly because of increased cost in the aspect of installations by increased layer constitutions of co-extruded films and provision of a coating line, etc., the demand cannot be satisfied also in the aspect of cost.
Further, in polyamide film, particularly nylon 6 film, the slippage characteristic and firmness (rigidity) will be lowered by moisture absorption under an environment of high humidity. Such lowering in rigidity may bring about troubles during post-working such as a lamination step, printing step, bag-making step, etc., and its improvement has been strongly demanded.
Of the above film characteristics, as the method for improving the slippage characteristic, there have been known the method to add metal soaps, bisamides, polyolefins, inorganic particles, etc., and among them addition of inert inorganic particles such as silicon dioxide, talc, kaolin, etc. is effective and practically applied. However, it is very difficult to improve lowering in rigidity of polyamide film by moisture absorption. For example, addition of talc or glass fibers will result in lowering in transparency and pinhole resistance, and also addition of a modified polyolefin and an ionomer resin which are low in moisture absorption, will still not only impair transparency, but also bring about lowering in the gas barrier property and rigidity.